1. Technical Field
The present invention relates to a nonaqueous conductive nanoink composition and more particularly, to a nonaqueous conductive nanoink composition which is suitable for forming conductive wirings and films with no cracks or delamination on a substrate by employing an anhydride compound.
2. Description of the Related Art
Noncontact direct writing technology through inkjet which is distinguished from the conventional optical patterning offers advantages in reduction of manufacturing costs and time since it allows ejecting an exact amount of ink to only a desired portion. For applying the inkjet method to form a metal wiring of a substrate, a metal ink has been greatly developed with growth of interests in the metal ink.
A method of forming conductive wirings or films generally includes coating or printing a conductive nanoink on a substrate, drying and sintering. Final conductivity is exhibited after the sintering process. The conductivity can be decreased (i) when a content of nanomaterial is low, (ii) when a content of remained organic compounds is high after sintering, (iii) when short/open due to cracks and/or delamination is caused after drying, or (iv) when short/open due to cracks and/or delamination is caused after sintering. When silver or copper is used as a conductive nanomaterial and the sintering is performed sufficiently, reasons (i) and (ii) may be avoid but electric current may be blocked or resistance may be too high due to electrical short associated with reasons (iii) and (iv).
A drying method of nanoink of a substrate includes (i) evaporation, (ii) densification and contraction, (iii) crack initiation due to contraction and non-fluidity, and (iv) crack and delamination. That is, when nanoink is dried on a substrate, contraction may be caused with increase of the concentration of nanoparticles in the nanoink by the evaporation of a solvent. A contact portion with air may be more contracted with more evaporation than the opposite portion to the air-contacted portion and this may cause crack for the contraction at the air-contacted portion. This crack may grow with the evaporation of the solvent and reach to the interface of the opposite portion to the air-contacted portion. As a result, if adhesion at the interface of the opposite portion to the air-contacted portion is not strong enough compared to the contraction stress, it may cause delamination.
Preventing cracks and improving adhesion between wiring and substrate are critical factors in the manufacturing metal nanoink composition and the development of metal nanoink composition which satisfies those factors is highly demanded.